The crash happened on Talley Road around 3:20 p.m. Monday. National Transportation Safety Board Chairman Christopher A. Hart said the bus had just left Woodmore Elementary School, but that the road was not the designated route of the bus. The NTSB said it was unclear why Walker took the road or if he had the same route before.

Investigators said the bus crash about a mile away from the school. Preliminary details suggests the bus left the roadway, overturned and collided with a utility pole and eventually coming to a mangled rest against tree in front of a home.

NTSB investigators said Talley Road is a two-lane roadway with a posted speed limit of 30 mph with lower speed advisories for the curves. In court papers, police said Walker was driving well over the posted speed limit when he lost control of the bus.

"It was just so horrible," said neighbor Elise Martin. "I heard him, that bus driver, hit the... hit that tree. He must been going fast because I heard because I heard the children when I opened my door they was crying you know and I looked over there and I went 'Oh, my god!'"

Of the 37 passengers on the 2008 Thomas Built bus, 23 were rushed to Children’s Hospital at Erlanger. Five students died at the scene. A sixth child died Wednesday evening.

Walker was arrested and charged with five counts vehicular homicide, reckless endangerment and reckless driving. Chattanooga Police Chief Fred Fletcher said more charges are likely as the criminal investigation progresses.

Garrett said police are continuing to interview witnesses and review video footage of the crash.

Public records indicate Walker has a history of traffic incidents, one involving another school bus he was driving which hit another vehicle. No injuries were reported in that case. Records also show Walker had his license suspended a few years ago for failing to provide proof of insurance. The NTSB said Walker obtained his commercial license in April.

Walker’s mother said her son called her after the crash and expressed to her that he hoped the crash was not his fault.

“My son called me as soon as it happened. He said 'I love you mom. I’ve been in a domestic accident aboard the bus.’ While he was trying to get the kids off, blood was everywhere, bodies everywhere, he was explaining and the phone disconnected,” said Gwenevere Cook, Walker's mother.

Meanwhile, the NTSB arrived on scene early Tuesday morning to conduct their own investigation. Hart said they are working with police to determine what caused the crash, but while the police are focusing on building a criminal case, the NTSB is concerned with making future school bus travel safer.

The NTSB said they will be inspecting the bus, its engine chip, and studying the operations record from both Hamilton County Schools and Durham School Services, which the district contracts to run the bus services. They will also be independently interviewing witness and the driver. They also plan to review the internal and external cameras on the bus, if the equipment wasn't too damaged.

Hart said the NTSB is bringing in a specialist to analyze video and audio recordings made on interior cameras that were damaged in Monday's wreck. Investigators are facing similar challenges in retrieving speed and braking information from the engine control module that has been removed from the bus.